The present invention relates to a fluid flow control valve, either a liquid flow control valve or a gas flow control valve.
The present invention relates in particular to a fuel flow control valve for a combustion chamber, especially a premixed lean burn combustion chamber, of a gas turbine engine. The fuel may be a gas fuel or a liquid fuel.
Combustion processes often generate noise, that is, they emit energy in the form of high frequency pressure perturbations. Combustion noise occurs in premixed lean burn combustion chambers of gas turbine engines. There is an energy interchange between the sound waves and the unsteady heat input to the combustion chamber which produces amplification of the combustion noise. This amplification of the combustion noise may result in sufficiently high amplitudes which may result in damage to the combustion chamber and gas turbine engine.
It has previously been proposed to reduce the combustion noise by controlling the unsteady heat release from the combustion chamber by modulation of the fuel supply about a mean level at a frequency, amplitude and phase shift determined from combustion noise pressure measurements. The fuel supply is modulated by a fluid flow control valve.
Accordingly the present invention seeks to provide a novel fluid flow control valve which reduces, preferably overcomes, the above mentioned problems.
Accordingly the present invention provides a fluid flow control valve comprising a valve seat, a valve stem, the valve seat has a passage therethrough for the flow of fluid, the valve stem and the valve seat are relatively movable towards or away from each other to control the fluid flow through the valve, a magnetostrictive element arranged to move the valve stem and the valve seat towards each other, biasing means to move the valve stem and the valve seat away from each other, a valve wall enclosing the valve stem, biasing means and magnetostrictive element, a magnetic coil arranged around the valve wall, a keeper arranged around the valve wall and a permanent magnet arranged around the valve wall.
Preferably the valve wall encloses [enclosing ] the valve seat.
Preferably the valve wall is cylindrical.
Preferably the valve seat, valve stem, magnetostrictive element, magnetic coil, permanent magnet, keeper and valve wall are arranged coaxially.
Preferably the biasing means comprises a spring, preferably a belleville spring.
Preferably the magnetostrictive element comprises an alloy of terbium, dysprosium and iron.
Preferably the valve wall comprises a low magnetic permeability material, preferably stainless steel or a titanium alloy. Preferably the stainless steel comprises 18 wt % chromium, 8 wt % nickel and balance iron, carbon and incidental impurities.
Preferably the permanent magnet is annular.
Preferably the keeper comprises magnetically soft iron or ferrite.
Preferably a cooling fluid is supplied through at least one passage between the valve wall and the magnetic coil to cool the valve.
Preferably the valve seat has a passage therethrough for the flow of the fluid and the magnetostrictive element has a passage therethrough for the flow of the fluid, the passage in the magnetostrictive element is in alignment with the passage in the valve seat such that the flow of fluid therethrough cools the valve.
Preferably the valve stem is movable towards or away from the valve seat to control the fluid flow through the valve, the magnetostrictive element is arranged to move the valve stem towards the valve seat, the biasing means is arranged to move the valve stem away from the valve seat.
The valve seat may be movable towards or away from the valve stem to control the fluid flow through the valve, a second magnetostrictive element is arranged to move the valve seat towards the valve stem, second biasing means to move the valve seat away from the valve stem, the valve wall also enclosing the second biasing means and the second magnetostrictive element, a second magnetic coil is arranged around the valve wall, a second keeper is arranged around the valve wall and a second permanent magnet is arranged around the valve wall.